1. Field of the Invention
Embodiments of the invention relate to an image display device capable of implementing a two-dimensional plane image (hereinafter referred to as ‘2D image’) and a three-dimensional stereoscopic image (hereinafter referred to as ‘3D image’).
2. Discussion of the Related Art
An image display device implements a 3D image using a stereoscopic technique or an autostereoscopic technique.
The stereoscopic technique, which uses a parallax image between left and right eyes of a user with a high stereoscopic effect, includes a glasses type method and a non-glasses type method, both of which have been put to practical use. In the glasses type method, the parallax image between the left and right eyes is displayed on a direct-view display or a projector through a change in a polarization direction of the parallax image or in a time-division manner, and a stereoscopic image is implemented using polarization glasses or liquid crystal shutter glasses. In the non-glasses type method, an optical plate such as a parallax barrier for separating an optical axis of the parallax image between the left and right eyes is generally installed in front of or behind a display screen.
As shown in FIG. 1, the image display device using the glasses type method may include a patterned retarder 5 for converting polarization characteristics of light incident on polarization glasses 6 on a display panel 3. In the glasses type method, a left eye image L and a right eye image R are alternately displayed on the display panel 3, and the polarization characteristics of light incident on the polarization glasses 6 are converted by the patterned retarder 5. Through such an operation of the image display device using the glasses type method, the left eye image L and the right eye image R may be spatially divided, thereby implementing a 3D image. In FIG. 1, a reference numeral 1 denotes a backlight unit providing light to the display panel 3, and reference numerals 2 and 4 denote polarizing plates respectively attached to upper and lower surfaces of the display panel 3 so as to select linear polarization.
In the glasses type method, visibility of the 3D image is reduced because of crosstalk generated at locations of vertical viewing angle. As a result, in the general glasses type method, a range of the vertical viewing angle, at which the user can view the 3D image with the good image quality, is very narrow. The crosstalk is generated because the left eye image L passes through an area of a right eye patterned retarder as well as an area of a left eye patterned retarder and the right eye image R passes through the area of the left eye patterned retarder as well as the area of the right eye patterned retarder at the locations of the vertical viewing angle. Hence, as shown in FIG. 2, Japanese Laid Open Publication No. 2002-185983 discloses a method for obtaining wider vertical viewing angle by forming black stripes BS in an area of a patterned retarder corresponding to black matrixes BM of a display panel to thereby improve visibility of the 3D image. In FIG. 2, when the user observes the 3D image at a predetermined distance D, a vertical viewing angle α, at which the crosstalk is not theoretically generated, depends on the size of the black matrixes BM of the display panel, the size of the black stripes BS of the patterned retarder, and a distance S between the display panel and the patterned retarder. The vertical viewing angle α widens as the size of the black matrixes BM and the size of the black stripes BS increase and the distance S between the display panel and the patterned retarder decreases.
However, the related art image display device including the black stripes has the following problems.
First, the black stripes of the patterned retarder, which are used to obtain the wide vertical viewing angle and improve the visibility of the 3D image, interact with the black matrixes of the display panel, thereby generating moiré. When a 2D image is implemented, the black stripes of the patterned retarder greatly reduce the visibility of the 2D image. FIG. 3 illustrates the moiré generated when observing, for example, a 47-inch image display device including black stripes at a location 4 meters away from the 47-inch image display device. As shown in FIG. 3, when the 2D image was implemented, moirés of 90 mm, 150 mm, and 355 mm were visible at observation locations A, B, and C, respectively.
Second, the black stripes of the patterned retarder, which are used to obtain the wide vertical viewing angle and improve the visibility of the 3D image, bring about a side effect resulting in a large reduction in a luminance of the 2D image. The side effect is generated because predetermined portions of pixels of the display panel are covered by a pattern of the black stripes as shown in FIG. 4(b). Accordingly, when the 2D image is implemented, an amount of transmitted light is reduced by about 30%, as compared to an image display device not including the black stripes as shown in FIG. 4(a).